Acute Kidney Injury (AKI) is a common clinical problem defined by an abrupt (< 48 hour) increase in serum creatinine (SCr) resulting from an injury or insult causing a functional or structural change in the kidney. Despite significant advancements in the care of the critically ill child, mortality rates in children who develop AKI have not improved. Using genomic and proteomic technologies, we identified neutrophil gelatinase-associated lipocalin (NGAL) as a biomarker that is produced in high levels in the kidney very early after kidney injury. We have developed three aims for these complementary studies: NGAL directed therapy to prevent AKI, NGAL directed therapy to optimize support for patients who develop AKI and biomarker/proteomic profiling to predict or detect CKD development early. Accordingly the specific aims of this proposal are: Aim 1. Prevent AKI - this aim will determine if the administration of fenoldopam to children at risk for AKI, based upon plasma NGAL point of care testing, will prevent the occurrence of AKI following CPB. AKI will be determined based on the modified pediatric RIFLE (pRIFLE) criteria. Using pRIFLE, AKI will be defined as an estimated creatinine clearance decrease by ? 25% from preoperative baseline level or urine output < 0.5 ml/kg/hr for 6 hours within 48h of surgery. Aim 2. Prevent acute complications of AKI - this aim will determine if persistently elevated NGAL can predict which critically ill children will ultimately develop significant (>10%) positive ICU fluid accumulation for more than 24 hours and thereby optimize dialysis initiation. Aim 3: Predict long term consequences of AKI - this aim will assess urinary proteomic profiles for discovery of novel biomarkers to predict the AKI recovery and/or transition of AKI to CKD. The multidisciplinary team of investigators, including pediatric nephrologists, intensivists, cardiologists, and biostatisticians will extensively employ the Proteomics Core (Core B) and the Biomarker Core (Core C) for the successful completion of this project.